The present invention relates to a wiring layer transfer composite used for the production of semiconductor packages and a method and an apparatus for producing such a wiring layer transfer composite.
Recently, the number of input/output terminals of a semiconductor device is increasing, as the level of integration of semiconductor chips increases. Thus, semiconductor packages having large numbers of input/output terminals have been demanded. The input/output terminals are generally classified into a type arranged in a row around the semiconductor package, and a type arranged in a large number of rows in a two-dimensional manner not only around the semiconductor package but also under it. In the former, the arrangement pitch of the input/output terminals should be decreased to increase their number, though connection between the input/output terminals and the wiring on a circuit board is difficult at a pitch of 0.5 mm or less. In the latter type, the input/output terminals can be arranged in a relatively large pitch, advantageous in increase in the number of input/output terminals.
In the latter arrangement of input/output terminals, there are a pin grid array (PGA) type having connection pins and a ball grid array (BGA) type. Because connection pins are inserted into opening-type terminals of a circuit board in the PGA type, it is not suitable for surface mounting. On the other hand, the BGA type enables surface mounting, suitable for the mounting of small, thin semiconductor packages in laptop computers, cellular phones, etc. Because these digital devices are increasingly miniaturized and made thinner, the pitch of pins used for semiconductor packages is becoming narrower.
Adopted to form connection pins of a BGA type is a method in which a thin copper foil is etched to provide wiring for semiconductor chips. It has been tried to make a wiring-forming copper foil as thin as about 1-18 xcexcm. However, when such a thin copper foil is used, it should be provided with enough rigidity to improve handling. Proposed for that purpose is, for instance, a method of attaching an aluminum carrier sheet to the copper foil. In such a simple two-layer structure, however, the carrier sheet per se needs to be made thicker, resulting in the problem that etching specks are likely to be generated by removal of the carrier sheet.
Under such circumstances, a transfer method disclosed in Japanese Patent Laid-Open No. 8-293510 has recently been attracting much attention as a method for forming wiring patterns for semiconductor packages. One example of this transfer method is shown in FIGS. 7(a)-(g). A Ni plating layer is formed as a barrier layer 2 on a carrier sheet 1 composed of a electrolytic copper foil (step (a)), and a dry photoresist film 4 is laminated thereon (step (b)). The dry photoresist film 4 is exposed to light in a desired pattern and developed to provide a laminate having recesses 4a for wiring pattern (step (c)). This laminate is immersed in a copper sulfate solution to carry out electrolytic copper plating (step (d)). Next, the resist layer 4 is removed by using a potassium hydroxide solution to provide a transfer foil laminate 6 having a three-layer structure in which a copper wiring pattern 3 is formed (step (e)). The transfer foil laminate 6 is set in a cavity of a molding die, into which a semiconductor-sealing epoxy resin is injected and cured, thereby embedding copper wiring in a cured epoxy resin layer 5 (step (f)). The carrier sheet 1 and the barrier layer 2 are removed by selective etching, thereby leaving only a copper wiring 3 in the cured epoxy resin layer 5 (step (g)).
When wiring having a thickness of 18 xcexcm or less is formed by this transfer method, a copper foil is used as a carrier sheet 1 for providing rigidity for easiness of handling. The barrier layer 2 is used for the purposes of (i) preventing an etching solution from reaching the carrier sheet 1 when the dry photoresist film 4 is etched to form a wiring pattern, and (ii) preventing an etching solution from reaching the wiring 3 when the carrier sheet 1 is removed by etching after embedding the copper wiring 3 in the cured epoxy resin layer 5. Accordingly, the barrier layer 2 should be made of a metal having different etchability from that of the wiring.
The above transfer method is advantageous in that etching specks are not likely to be generated on a wiring copper foil transferred to a semiconductor-sealing epoxy resin, because the barrier layer is selectively etched after the carrier sheet 1 is selectively etched. However, because it is a method in which a wiring is produced by forming a Ni plating layer in recesses 4a generated by the etching of a dry photoresist film 4, its steps are complicated.
To solve the above problem, the inventors have investigated the production of a wiring layer transfer composite having a three-layer structure by pressure-welding a copper foil for a carrier layer and a copper foil for a wiring-forming layer via a barrier layer by a high-speed continuous bonding method such as rolling, etc. As a result, it has been found that because the barrier layer 2 is as extremely thin as 1 xcexcm or less, the barrier layer 2 is broken at the time of pressure welding such as rolling for producing a wiring layer transfer composite.
Accordingly, an object of the present invention is to provide a wiring layer transfer composite having a barrier layer as extremely thin as 1 xcexcm or less without breakage, and a method and apparatus for producing such a wiring layer transfer composite.
As a result of intense research in view of the above object, it has been found that a wiring layer transfer composite constituted by a laminate composed of a wiring-forming layer, a barrier layer and a carrier layer can be obtained substantially without generating defects such as breakage in the barrier layer, by making the average surface roughness Rz of the wiring-forming layer and the carrier layer as small as 5 xcexcm or less, by forming as extremely thin a barrier layer as 1 xcexcm or less in an average thickness on at least one of the wiring-forming layer and the carrier layer, and by pressure-welding the wiring-forming layer and the carrier layer via the barrier layer. The present invention has been completed based on this finding.
Thus, the wiring layer transfer composite according to the present invention is constituted by a laminate composed of a Cu-based carrier layer having an average thickness of 50 xcexcm or less, a barrier layer made of a metal having different etchability from that of Cu and having an average thickness of 1 xcexcm or less, and a Cu-based, wiring-forming layer having an average thickness of 20 xcexcm or less, the barrier layer being a continuos layer substantially free from defects.
Each of the carrier layer and the wiring-forming layer preferably has an average surface roughness Rz of 5 xcexcm or less in both surfaces. Each of the carrier layer and the wiring-forming layer is preferably made of substantially pure copper. The barrier layer is preferably a plating or vapor deposition layer of nickel.
The composite metal foil according to the present invention is constituted by a laminate composed of a first metal foil based on Cu and having an average thickness of 50 xcexcm or less, a barrier layer made of a metal having different etchability from that of Cu and having an average thickness of 1 xcexcm or less, and a second metal foil based on Cu and having an average thickness of 20 xcexcm or less, the barrier layer being a continuous layer substantially free from defects.
The first method for producing a composite metal foil according to the present invention comprises the steps of (a) plating a metal having different etchability from that of Cu onto the first metal foil or the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; (b) conducting an activation treatment onto a surface of the barrier layer and a surface of the first or second metal foil on which the barrier layer is not formed; and (c) pressure-welding both metal foils in such a manner that the activated surfaces are facing each other.
The second method for producing a composite metal foil according to the present invention comprises the steps of (a) vapor-depositing a metal having different etchability from that of Cu onto the first metal foil or the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; (b) heating both of the first and second metal foils to a temperature of 300xc2x0 C. or higher; and (c) pressure-welding both metal foils via the barrier layer.
The third method for producing a composite metal foil according to the present invention comprises the steps of (a) vapor-depositing a metal having different etchability from that of Cu onto at least one of the first metal foil and the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; and (b) pressure-welding both metal foils via the barrier layer.
The first method for producing a wiring layer transfer composite according to the present invention comprises the steps of (a) preparing a first Cu-based metal foil having an average thickness of 50 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a carrier layer; (b) preparing a second Cu-based metal foil having an average thickness of 20 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a wiring-forming layer; (c) plating a metal having different etchability from that of Cu onto the first metal foil or the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; (d) conducting an activation treatment onto a surface of the barrier layer and a surface of the first or second metal foil on which the barrier layer is not formed; and (e) pressure-welding both metal foils in such a manner that the activated surfaces are facing each other. The activation treatment is preferably ion etching.
The second method for producing a wiring layer transfer composite according to the present invention comprises the steps of (a) preparing a first Cu-based metal foil having an average thickness of 50 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a carrier layer; (b) preparing a second Cu-based metal foil having an average thickness of 20 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a wiring-forming layer; (c) plating a metal having different etchability from that of Cu onto the first metal foil or the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; (d) heating both of the first and second metal foils to a temperature of 300xc2x0 C. or higher; and (e) pressure-welding both metal foils via the barrier layer.
The third method for producing a wiring layer transfer composite according to the present invention comprises the steps of (a) preparing a first Cu-based metal foil having an average thickness of 50 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a carrier layer; (b) preparing a second Cu-based metal foil having an average thickness of 20 xcexcm or less and an average surface roughness Rz of 5 xcexcm or less in both surfaces for a wiring-forming layer; (c) vapor-depositing a metal having different etchability from that of Cu onto at least one of the first metal foil and the second metal foil to form a barrier layer having an average thickness of 1 xcexcm or less; and (d) pressure-welding both metal foils via the barrier layer. The barrier layer is preferably formed by vacuum vapor deposition.
In any production methods, the pressure welding is carried out by rolling at a draft of 2% or less.
The apparatus for producing a composite metal foil according to the present invention comprises a vacuum chamber, a vapor deposition means disposed in the vacuum chamber, a pair of guide rolls disposed in the vacuum chamber at a position opposite to the vapor deposition means, and pressure rolls for continuously pressure-welding a first metal foil and a second metal foil which are subjected to vapor deposition while passing over the guide rolls, in such a manner that vapor-deposited surfaces of the first and second metal foils are opposing each other.